Method of liquid withdrawal from a tool spindle

ABSTRACT

A method for withdrawing liquid from the liquid bearings of a spindle ( 1 ) carried in liquid bearings ( 3, 5 ) distinguished in that with the help of pressurised gas, the liquid, together with the gas, is forced to exit the spindle during the operation of the spindle via at least one first channel ( 12 ), and that when the spindle is shut down, is forced to exit via at least one second channel ( 13 ) with a smaller flow-through cross-section than the first channel.

[0001] The present invention relates to a method of withdrawing liquidfrom the liquid bearing and cooling system of a spindle carried inliquid bearings.

[0002] When using a liquid bearing, i.e. a bearing in which the playbetween the fixed and the rotating parts is occupied by a continuoussupply of liquid, for example water, there normally exists a need tolimit in a controlled way the spread of the liquid in the spindle.During the operation of the spindle, liquid under pressure is thussupplied to the said play, which means that the liquid will leak outfrom both sides of the bearing. With the help of pressurised gas from asource of pressurised air, for example air, so-called blocking gas, thespreading of the liquid can be controlled and continuously removed fromthe spindle. In this context, reference is made, for example, to theSwedish application 9901053-0 that discusses a tool spindle. Coolingliquid can also be supplied to the spindle.

[0003] During the operation of the spindle, there thus exists anessentially constant and continuous state with an effective bearingfunction and, whenever applicable, cooling. The present inventionrelates to a completely new method of withdrawing liquid from thespindle with the help of blocking gas. The total flow of gas and liquidis naturally determined by the size and number of bearings as well asthe cooling need, and thus requires one or more withdrawal channels witha sufficient cross-sectional flow.

[0004] When the spindle is shut down and the flow of liquid stopped,there is a desire to completely empty the spindle of remaining liquid.As the exhausting channel normally extends up to a higher level than theactual spindle, the spindle cannot be emptied by the forces of gravitywhen collecting the liquid.

[0005] According to the invention, emptying takes place with the help ofthe pressurised blocking air. The flow cross-section of the withdrawalchannel is adapted for operating conditions with a large flow volume(liquid and gas). The significantly reduced flow of a shut-down tool,i.e. the gas flow with remaining liquid, means that the rate of flow inthe exhausting channel becomes low with an equivalent low pressure,which leads to an insufficient capacity for emptying. However, byarranging a special withdrawal channel with a flow cross-section, lessthan that of the first named channel, to be used with a shut-downspindle at the same time as the first named channel is closed off, asufficient rate of flow is obtained, which leads to that practicallycomplete emptying of the liquid is achieved. The gas/liquid mixtureintended for withdrawal is collected in an area located lower down inrelation to the orientation of the spindle in space.

[0006] The effective removal of liquid from a liquid-borne spindle isachieved with the help of the invention, as is evident from thecharacterising sections of the claims.

[0007] The invention will be described in more detail in the form ofexamples with reference to the drawing that shows schematically alongitudinal cross-section of a spindle equipped with features thatsolve the practical aspects of the invention.

[0008]1 designates the stationary part of the spindle shown as anexample, i.e. the part that is firmly attached in the machine of whichthe spindle forms a part. This stationary unit 1 has a spindle axle 2that is supported so that it can rotate, partly by two radially actingliquid bearings 3 and partly by a double-acting axial liquid bearing 5that acts on both sides of the flange-like part 4 of the spindle andwhere one forms part of the left radial bearing as seen in the figure.Here, the term liquid bearing refers to a bearing with a static functionor dynamic function or a combination of these liquid bearing principles.The spindle axle 2 is driven by an electric motor whose stator isdesignated with 6 and rotor with 7.

[0009] The liquid for the liquid bearings 3 and 5, and for the coolingsystem of the spindle, is supplied to the spindle via channels that arenot shown here but where reference is instead made to that previouslyknown via the previously named Swedish patent 9901053-0. Area 8 is anarea that is used for transferring media from the stationary part to therotatable spindle axle 2.

[0010] Gas, for example air from a pressurised source (not shown), issupplied to the spindle via one (or more) supply channels 9 from wherethe pressurised gas is led to the liquid space 10 in which the bearingand cooling liquid are collected under the shaft of the spindle. Anoutlet 11 leads from the liquid space 10 to a removal channel 12 to leadaway the pressurised gas together with the bearing and cooling liquidduring the normal operation of the spindle. To retain the pressure inthe bearing and cooling area, the said outlet 11 has a significantlysmaller flow-through area than the inlet (here not designated with areference number) from the supply channel 9.

[0011] The removal channel 12 has a flow-through cross-section adaptedfor leading away liquid and gas supplied to the spindle during itsoperation. The flow of gas adapted to the operation, and thus the gaspressure for leading away the liquid from the spindle through theremoval channel 12, becomes insufficient when the spindle is shut downand the flow of liquid supplied to the spindle significantly decreasesand ceases. The pressure and thus the rate of flow of the gas aretherefore insufficient to force the remaining liquid that has collectedin the lower part of the spindle out through channel 12. To establish arate of gas flow able to empty the spindle of liquid, a second removalchannel 13 is therefore arranged with a significantly smallerflow-through cross-section that is adapted for this purpose. In thefigure, this second channel 13 is shown running inside the first channel12. When the spindle is shut down, the first channel 12 is closed offwith the help of a valve 14 so that the total flow is led through thesecond channel 13. As the channel 13 is built inside the first channel12, the second channel is shown shunted (at 15) when passing the valve14. The inlet 16 of the second channel 13 in the spindle should bepositioned essentially in the lowest located area of the spindle inorder to be thus able to empty the spindle of, in practical terms, allliquid.

[0012] It should be pointed out that the second channel 13 need not belocated within the first channel 12, which in turn need not necessarilyhave its inlet located at the lowest located area of the spindle. One ormore first and second channels can occur within the spindle.

1. Method for withdrawing liquid from the liquid bearings of a spindle(1) carried in liquid bearings (3, 5) characterised in that with thehelp of pressurised gas, the liquid, together with the gas, is forced toexit the spindle during the operation of the spindle via at least onefirst channel (12) and, when the spindle is shut down, is forced to exitvia at least one second channel (13) with a smaller flow-throughcross-section than the first channel.
 2. Method according to claim 1characterised in that with the help of the pressurised gas, the liquidis forced into an area located down in the lower part in relation to theorientation of the spindle in space within which the inlet (16) for thesecond channel (13) is located, and that during shut-down of thespindle, the first channel (12) is closed off by means of a closurevalve (14).
 3. Method according to claim 1 or 2 characterised in thatthe second channel (13) is wholly or partly accommodated in the firstchannel (12).
 4. Method according to any of claims 1-3 characterised inthat air is used as the gas.